[TenTec] Omni VI problem

[Mike]

Greetings everybody.
After nearly 7 years of trouble-free service my Omni VI has suddenly
developed a strangeness!

Working into either a properly matched antenna, or into a dummy load. at any
power & on any band, I get very irregular swr readings - both on the Omni's
meter & on an external Autek WM1. This occurs only on the Omni & not on any
other rig used in identical set-up.
At the same time the Omni's internal meter, when switched to read 'FWD',
reads full-scale on both Tx & Rx & on all bands/modes etc.
I do not have any 'AUX' antenna, but, when I actuate the 'AUX' switch, the
external WM1 swr meter reads ok (i.e. nil swr reading & power normal), the
Omni's meter still reads full-scale continuously on FWD, and the SWR
readings (jumps) disappear.
I've removed the Low Pass Filter board, & the PA, & all components on both
are ok.
If I pull plug 35 from the 9mHz  mixer/IF board, the FWD meter pointer drops
to zero. On this plug (35), I get the following voltages...

                       Tx.             Rx.
Reg +               9.4v          9.4v
T                     10.3v          1.5v
R                       0.7v           7.5v

If I measure from the front-panel meter to ground, whilst in FWD position, I
get 0.45v.

Has anybody had a similar problem, and, even if not, please, do any of you
Omni experts out there have any (worthwhile) suggestions?
Thanks & 73 de Mike, zl1mh.